Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $23.62   13.266%   $26.7534   $26.75   $26.75   $26.80  
  Purchase #2 $246.70   9.272%   $269.574   $269.57   $269.55   $269.60  
  Purchase #3 $113.33   5.161%   $119.179   $119.18   $119.20   $119.20  
  Purchase #4 $131.74   11.816%   $147.3064   $147.31   $147.30   $147.30  
  Purchase #5 $39.34   3.147%   $40.578   $40.58   $40.60   $40.60  
  Purchase #6 $60.38   9.778%   $66.284   $66.28   $66.30   $66.30  
  Purchase #7 $178.60   10.646%   $197.6138   $197.61   $197.60   $197.60  
  7 purchase totals = $793.71       $867.2886   $867.28   $867.30   $867.40